Cylindrical fiber coupling lens with biaspheric surfaces

ABSTRACT

A cylindrical lens for coupling light from a line of emitting facets of laser diodes to a line of entrance faces of respective fiber waveguides. The lens is biaspheric, i.e., it includes two aspheric refractive surfaces which, in planes transverse to the lens axis, have curvatures that are other than of a conic in cross-section. The surfaces are shaped to correct for spherical aberrations, coma, and other off-axis aberrations. A system places the lens to image the emitting facets of the laser diode line onto the entrance facets of the fiber waveguides so that coupling efficiency between the two is relatively insensitive to lateral misalignment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 07/993,653, filed Dec. 18,1992.

This application is related to the concurrently filed and commonlyassigned application of Hong Po and Stephen D. Fantone entitled "OpticalFiber Laser and Geometric Coupler".

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to laser systems in which cylindrical lensescouple the outputs of laser diodes into optical fiber waveguides toprovide pump light for lasing action in laser cavities and particularlyto cylindrical lenses for coupling light from laser diode arrays intooptical fiber waveguides.

2. Background of the Prior Art

Various means have been used to couple light from arrays of alignedlaser diode stripes into optical fiber waveguide ends for the purpose ofpumping solid state lasers. U.S. Pat. Nos. 4,818,062, 4,479,224,4,383,318, and 4,911,526 disclose butt coupling light from laser diodearrays into optical fiber waveguide ends by placing the emitting facesof the laser diodes as close as possible to the entrance faces of theoptical fiber waveguides. However, butt coupling makes it difficult toachieve high coupling efficiency because of the large angulardivergences of laser diode stripes, at least in one azimuth, comparedwith the numerical aperture of the optical fiber waveguide in the sameazimuth. Efficient coupling in these circumstances also requirescritical close spacing and alignment of the members and/or fibercladding having very low refractive indices. The close spacing alsorisks damage to the members.

U.S. Pat. No. 4,972,427 discloses coupling of laser diodes in a laserbar into a slab of a Talbot cavity using a lenticular array aligned withthe diodes and a cylindrical lens behind the lenticular array. Thispasses light into the slab but apparently does not simplify attainmentof greater efficiencies.

U.S. Pat. No. 5,127,068 discloses coupling the output of laser diodesinto optical fiber waveguides by collimating the output emissions of thelaser diodes with a cylindrical optical fiber having a diameter roughlyequal to the diameter of the optical fiber waveguides to be coupled toand preferably 20% to 50% larger than the lateral dimension of the laserdiode emitter regions. The patent discloses spacing the optical fiberend from the microlens as closely as possible and also suggests thatcross-sections such as elliptical and hyperbolic could be useful forcorrection of particular spherical aberrations.

However, no matter how close one places such fiber waveguides to such acollimating lens, off axis rays may still fall outside the acceptanceangle of the fiber waveguides. Moreover, cylindrical fiber lenses withround or other conic cross-sections may correct well on-axis but quicklydegrade off-axis. This affects coupling efficiency adversely.

U.S. Pat. No. 4,826,269 discloses focusing diode lasers onto a singleregion by circularly disposing a number of vertical and horizontalcylindrical lenses. The complexity of such a device makes it unsuitablefor many applications.

U.S. Pat. No. 5,081,639 discloses a method of making a cylindricalmicrolens which produces focused, defocused, or collimated exiting lightand having circular, elliptical, and hyperbolic cross-sectional shapes.Such lenses are also well-corrected on-axis but rapidly degradeoff-axis. Thus, they have limited ability to couple light simply andefficiently from laser diodes into fiber waveguides.

Furthermore, such small-fiber cylindrical lenses tend to sag. This makesit difficult to align them with the diodes and the optical fiber ends.

An object of this invention is to avoid these disadvantages.

Another object is to improve laser systems.

Another object of the invention is to improve coupling of light fromlaser diodes to optical fiber waveguides.

Yet another object of the invention is to furnish cylindrical lenses forefficient coupling of light from laser diodes into optical fiberwaveguides.

Still another object of the invention is to improve manufacturingmethods and means for such cylindrical lenses.

Yet another object of the invention is to improve systems for generatinglight for pumping solid state lasers.

Other objects of the invention will, in part, appear hereinafter and, inpart, be obvious when the following detailed description is read.

SUMMARY OF THE INVENTION

The invention comprises a system for coupling laser diodes to fiberwaveguides. The system includes a cylindrical biaspheric magnifying lenshaving a diameter substantially larger than either the laser diodes orthe optical fiber waveguides. The biaspheric lens focuses the light fromthe diodes onto a substantial portion of the ends of the fiberwaveguides.

The terms "aspheric" and "biaspheric" are used herein in the sense thatthe lens cross-sectional surface in planes transverse to its cylindricalaxis are aconic (i.e., not circular, elliptical, hyperbolic, nor anyconic section). The term "aspheric" is used here in a more limitedsense. Described otherwise, the biaspheric cylindrical lens as used herehas two surfaces whose cross-sections follow paths other than those ofconic sections. For simplicity, these sections are also called"aconic-sections".

More specifically, according to the invention, the lens comprises atransparent material with two surfaces each defined by a straight linemoving parallel to an axis along respective curves other thanconic-section curves.

According to an aspect of the invention both surfaces together cooperateto correct for coma and other off-axis abberations but neither surfacealone corrects for these.

According to another feature of the invention, the on-axis aberrationsare balanced off against the off-axis aberrations to provide acorrection over a wide field.

According to another feature of the invention, the cylindrical lensincludes integral stiffening extensions at the portion.,; between thecylindrical surfaces.

According to still another feature of the invention, the stiffeningextensions project transversely relative to a plane separating thecylindrical surfaces.

According to yet another feature of the invention, the stiffeningextensions project along a plane separating the cylindrical surfaces.

According to still another feature of the invention, the stiffeningextensions project both transverse to and parallel to a plane separatingthe cylindrical surfaces.

According to another feature of the invention a laser light generatingsystem includes a biaspheric, cylindrical lens, i.e., one whosecross-sectional shapes follow paths other than conic sections, forcoupling light from an aligned plurality of laser diode sources to aplurality of optical fiber waveguides having ends aligned with thesources.

According to another feature of the invention, a method of forming thecylindrical lens comprises shaping a biaspheric cylindrical lens blockat a scale larger than the desired dimensions of the lens and afterwardsdrawing down the block to the desired dimensions of the lens, preferablyat a scale of 50 to 1.

According to another aspect of the invention, the biaspheric cylindricallens images the emitting facets of the laser diode array onto or intothe end faces of the optical fiber waveguides by directing the rays fromthe laser diode arrays so that they converge in an angle smaller thanthe acceptance angle of the fiber waveguides at their end faces in thesame azimuth.

These and other features of the invention are pointed out in the claims.Other objects and advantages will become evident from the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The principles of the present invention may be clearly understood byconsidering the following detailed description when read in conjunctionwith the accompanying drawings wherein:

FIG. 1 is a diagrammatic perspective view, with parts broken away, of alaser light coupling system according to the invention using abiaspheric cylindrical lens;

FIG. 2 is a diagrammatic plan view of the system in FIG. 1;

FIG. 3 is a sectional view of the lens of the system of FIGS. 1 and 2taken in the y-z plane;

FIG. 4 is a diagrammatic representation of a laser system using thecoupling system including the biaspheric cylindrical lens of FIGS. 1, 2,and 3;

FIGS. 5, 6, and 7 are graphs of the tangential ray displacement errorsof the biaspheric cylindrical lens in FIGS. 1 to 3 for different angularfield positions with the full field at 1.0;

FIGS. 8, 9, and 10 are graphs of the tangential and sagittal opticalpath differences of the biaspheric cylindrical lens in FIGS. 1 to 3,again as a function of field position;

FIGS. 11 and 12 are respective diagrammatic perspective views with partsbroken away illustrating means for carrying out a step in the methodaccording to the invention and showing numerically controlled machinetools cutting the edges of wheels for in turn, cutting enlarged profiles(50 ×) of the front and rear aspheric surfaces of the biaspheric lens inFIGS. 1 to 3;

FIGS. 13 and 14 are respective diagrammatic perspective views with partsbroken away illustrating means for carrying out a step in the methodaccording to the invention and showing a diamond plated wheel edgegrinding an aspheric surface as a cylindrical glass block;

FIG. 15 is a diagrammatic perspective view with parts broken away ofmeans for carrying out a step in the method according to the inventionand showing a numerically controlled machine tool cutting the edges of awheel with a 50× enlarged profile of the front aspheric surface of thebiaspheric lens in FIGS. 1 to 3;

FIG. 16 is diagrammatic sectional view of pad: of a wheel in FIG. 15;

FIG. 17 is a diagrammatic perspective view with parts broken away ofmeans for carrying out a step in the method according to the inventionand showing a grinding arrangement for cutting a groove for receiving a50× enlarged shape corresponding to a surface of the lens in FIGS. 1 to3;

FIG. 18 is a diagrammatic elevational view with parts broken away ofmeans for carrying out a step in the method according to the inventionshowing a block having an enlarged surface corresponding to a surface ofthe lens in FIGS. 1 to 3 and sitting in the groove formed by thearrangement in FIG. 21;

FIG. 19 is a diagrammatic perspective and partially schematic view withparts broken away of means for carrying out a step in the methodaccording to the invention and showing a grinding system which uses agrinding wheel having a cross-section complementary to the other surfaceof the biaspheric lens in FIGS. 1 to 3 on a 50× scale for grinding theother surface of the block in FIG. 18;

FIG. 20 is a diagrammatic perspective and partially schematic view withparts broken away of means for carrying out a step in the methodaccording to the invention and showing the grinding system of FIG. 19grinding the other surface of the block in FIG. 19;

FIG. 21 is a diagrammatic illustration showing means for carrying out astep in the method according to the invention and showing a drawingfurnace for drawing down the lens shaped block in FIGS. 17 and 18 into alens of smaller scale reduced in size by 50 to 1;

FIG. 22 is a diagrammatic perspective view of a portion of another lensembodying the invention and having cylindrical refracting surfacesshaped and spaced identically to the lens of FIG. 1, but with stiffeningextensions between the cylindrical surfaces;

FIG. 23 is a diagrammatic perspective view of part of yet another lensembodying the invention and having refracting surfaces shaped and spacedidentically to .the lens of FIG. 1, but with integral stiffeningextensions;

FIG. 24 is a diagrammatic perspective view of part of another lensembodying the invention with refracting surfaces corresponding to thelens of FIGS. 1, 2, and 3, with other stiffening extensions;

FIG. 25 is a diagrammatic perspective view with parts broken awayshowing a grinding wheel arrangement shaping one side of the lens ofFIG. 24;

FIG. 26 is a diagrammatic perspective view with parts broken awayshowing formation of a groove to receive the ground side of the lens inFIG. 29; and

FIG. 27 is a diagrammatic perspective view with parts broken awayshowing formation of the other refractive surface of the lens in FIG.21.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 2 show diagrammatic perspective and plan elevational viewsof a laser pumping system 8 embodying the invention and FIG. 3 shows anelevational view of a lens 10 employed in system 8 and also appearing inFIGS. 1 and 2. These figures are drawn relative to x, y, and z axes ofan orthogonal coordinate system as shown. In FIGS. 1, 2, and 3, abiaspheric cylindrical lens 10 couples light emerging from a lineararray of adjacent rectangular light emitting facets or ends 14 ofadjacent laser diodes 18 on a laser diode array or strip 20 ontorespective rectangular receiving ends 24 of a set of an equal number offlat adjacent optical fiber waveguides 28. The diode strip 20 isapproximately 100 μ wide, and the laser diode emitting facets 14 areapproximately 1 μ to 2 μ high in the y-direction, and approximately 5 μwide in the x-direction. The set of fiber waveguides 28 measured alongthe receiving ends 24 is also approximately 100 μ wide, and thereceiving end dimensions are approximately 5 μ to 15 μ high in they-direction and 5 μ wide in the x-direction.

The lens 10 extends along an axis 30 coincident with the x-axis andpreferably parallel within acceptable limits to the direction of thealignment of the centers of the adjacent laser diode emitting ends 14and centers of the adjacent optical fiber waveguide receiving ends 24. Afront surface 34 and a back surface 38 of the lens 10 run generallyparallel to the x-axis 30. The surfaces 34 and 38 are aspheric in they-z plane transverse to the x-axis 30. That is, the aspheric surfaces 34and 38 are each defined by a line extending parallel to the x-axis 30and travelling along a curved aconic path understanding that an "aconic"path is one other than the path of a conic section. The cross-sectionsof the surfaces 34 and 38 serve to limit spherical aberration, coma, andoff-axis aberrations as the lens 10 directs the light emerging from theends 14 so that it converges onto or in the ends 24.

Preferably, the centers of the entrance ends 24, the x-axis, and thecenters of the emitting facets 14 all lie in the x-z plane. For thispurpose, a suitable support 44, shown only diagrammatically, holds thelens 10, the strip 20, and the fiber waveguides 28 relative to eachother in a well-known manner.

FIG. 3 is an enlarged diagrammatic elevational view of the lens in FIGS.1 and 2 showing light rays 46 emerging from a typical laser diodeemitting end 14, undergoing refraction at the surfaces 34 and 38 of thelens 10, and entering a typical receiving end 24 of the fiber waveguides28. The lens 10 in the embodiment illustrated in FIGS. 1, 2, and 3 issubstantially larger in the direction of the vertical y-axis than eitherthe diode ends 14 or the receiving ends 24 of the fiber waveguides 28.This simplifies focusing and affords the lens 10 structural rigidityalong the direction of the x-axis 30 to limit the lens from sagging inthe x-y plane.

The lens 10 also includes flanges 52 at the top and bottom. These add tothe rigidity of the lens in the x-y plane by adding to its moment ofinertia in the y-z plane.

In general, the lens 10 furnishes an approximately 3 to 1 magnificationto converge the light emerging from the ends 14, which are approximately1 μ to 2 μ in the vertical direction, onto or into the fiber waveguidereceiving ends 24, which are 5 μ to 10 μ high. The lens 10 iswell-corrected not only on-axis, but off-axis as well, as measured inthe y-z plane.

Further details of a more specific embodiment of the invention appear inthe following table where, as best shown in FIG. 3, a distance TH0represents the axial distance from the laser diode ends 14 to theaspheric surface 34 (measuring along the z-axis); a distance TH1represents the axial thickness of the lens 10 along the z-axis; adistance TH2 represents the axial distance from the aspheric surface 38to the receiving ends 24 of the fiber waveguides 28 along the z-axis;the radius R₁ is the base radius of the surface 34 in the y-z plane,transverse to the x-axis 30; the radius R₂ is the base radius of thesurface 38 in the y-z plane, transverse to the x-axis; EFL is theeffective focal length of the lens the back focal length is BFL; thetransverse magnification in the y-z plane is T-MAG; n is the refractiveindex of the material of the lens 10; and F/# is the F-number of thelens 10 in the y-z plane. A positive radius has its center of curvatureto the right of the surface, and a negative radius has its center ofcurvature to the left of the surface.

The reference object height is REF OBJ HT; the reference aperture heightis REF AP HT; the length from the ends 14 to the ends 24 is LENGTH. Alldistances are measured in min.

The conic constant of surfaces 34 and 38 is K.

The shape of the aspheric surface in the y-z plane is expressed by thefollowing: ##EQU1## where K is the conic constant, c is the curvature1/R, with R the radius, at the pole of the surface, y and z are measuredfrom local coordinate systems having their origins at the pole of thesurfaces;

A, B, C, D, E, F, and G are 4th, 6th, 8th, 10th, 12th, 14th, and 16thorder coefficients for the surface.

In a specific embodiment, the following values apply:

TH0=0.071 mm

TH2=0.331 mm

TH1=0.098 mm

R₁ =0.206 mm

R₂ =-0.087 mm

n=1.830

EFL=0.087 mm

BFL=0.331 mm

T-MAG=-3.030 mm

F/#=1.820

REF OBJ HT=0.005 mm

REF AP HT=0.059 mm

LENGTH=0.500 mm

The coefficients in the equation above, for the surface 34 are:

K=-13.7971

A=-1.20030E+02, 4th order coefficient

B=5.04869E+04, 6th order coefficient

C=-2.41203E+07, 8th order coefficient

D=7.68848E+09, 10th order coefficient

E=-1.176771000E+12, 12th order coefficient

F=8.924943727E+13, 14th order coefficient

G=-3.058562317E+15, 16th order coefficient

The aspheric polynomial data for the surface 38 are:

K=-1.83326

A=-1.38769E+02, 4th order coefficient

B=1.05988E+04, 6th order coefficient

C=-7.64537E+05, 8th order coefficient

D=2.06031E+08 10th order coefficient

E=-1.205466504E+11, 12th order coefficient

F=2.591516650E+13, 14th order coefficient

G=-1.553182640E+15, 16th order coefficient

The above data is for a wavelength of 1.06 micrometers. Theserelationships result in a well-corrected lens not only on-axis but alsooff-axis in the y-z plane.

FIG. 4 illustrates a laser system L including the system 8 of FIGS. 1 to3 embodying the invention. Here, the lens 10 converges light from thediodes 18 onto the ends 24 of fiber waveguides 28. The latter form abundle at their distal, i.e. emitting, ends. Suitable optics 48, such asa lens converges the output of the fiber waveguides 28 into a solidstate laser cavity 50 which in a known manner produces a laser beam 51.Such a laser L is disclosed in the concurrently filed and commonlyassigned application of Hong Po and Stephen D. Fantone and entitled"Optical Fiber Laser and Geometric Coupler." In operation, the diodes 18generate light, and the lens 10 focuses the light on or into thereceiving ends 24 of the fiber waveguides 28. The light is guided to theemitting ends of the waveguides 28. The optics 48 converge the output ofthe fiber waveguides 28 into the solid state laser cavity 50. The lattergenerates a laser beam 51.

The aberrations of the aforementioned embodiments in the y-z planeappear in the graphs of FIGS. 5 to 10. In each graph, the maximumentrance pupil coordinate is normalized to 1.0. The horizontal axisrepresents the entrance pupil and the vertical axis represents theamount of aberration. FIGS. 5, 6, and 7 are graphs of the tangential raydisplacement errors of the biaspheric cylindrical lens in FIGS. 1 to 3for different decimal fractions of the full field, namely 1.00, 0.70,and 0.00.

The lens images the light outputs of laser diode arrays onto the endfaces of the optical fiber waveguides. More generally, the lens 10converges the rays from the laser diodes 18 onto the end faces 24 of thefiber waveguides 28 so the rays are channeled into an angle smaller thanthe acceptance angles of waveguides at their end faces 24. Theacceptance semifield angle in air is equal to:

    θ=sin .sup.-1 (NA)                                   (2)

where NA=the numerical aperture of the optical fiber waveguide in thedirection transverse to its width.

The lens 10 corrects for coma and off-axis aberrations in a distinctiveway. Specifically, each surface 34 and 38 is not individually corrected,but the combination of the two surfaces is. In the lens 10, the overallsystem is corrected for off-axis aberrations, especially coma,regardless of the correction of the individual surfaces, and the on-axisaberrations are balanced off against the off-axis aberrations to obtaina better correction over a wide field. In the embodiment disclosed, thelens 10 uses its 16th order polynomial to obtain this desiredcorrection. According to other embodiments of the invention, the lens 10may be constructed with higher or lower ordered polynomials, dependingon the desired numerical aperture.

The process of making the lens 10 appears in FIGS. 11 to 16. It involvesforming a larger preform block from the material comprising the lens 10.The larger block is identical in geometry to the lens 10, but on a 50×enlarged scale. The manufacture starts by shaping grinding wheels asshown in the views of FIGS. 11 and 12. In FIG. 11, a drive 52numerically controls a tool bit 54 which cuts into edge 58 of a rotating8 inch diameter steel wheel 60. The drive 54 rotates the wheel 60 andmoves the tool 54, radially and axially, relative to the axis of thewheel 60 to give the edge 58 a cross-sectional shape nearlycomplementary to the cross-sectional profile of the surface 34 of thelens 10, but on a 50× enlarged scale. Sufficient room is left on theedge 58 so that a later plating step brings the edge to across-sectional profile more exactly complementary to the surface 34 onthe 50× scale. The cut is repeated on another round steel blank toproduce a second wheel 60 like the first steel wheel 60.

In FIG. 12, the drive 52 rotates another 8 inch diameter wheel 68 andmoves the tool 54, axially and radially, relative to the axis of thewheel 68 to provide its edge with a shape nearly complementary to the50× enlarged axially transverse cross-sectional profile of the secondsurface 38 of the lens 10. Sufficient room is left on the edge 68 sothat a later plating step brings the edge to a cross-sectional profilemore exactly complementary to the surface 38 on the 50× scale. The drive52 and tool 54 repeat the process to form a second wheel 68 like firstwheel 68.

A plater, not shown, then plates the edge 58 of one wheel 60 and theedge 64 of one wheel 68 with coarse diamond particles. In the platedcondition, the cross-sections of the wheels are ideally exactlycomplementary to the surfaces 34 and 38 on an enlarged 50× scale. Tosimplify the grinding process, the plater also plates the outerperipheral side surfaces of the wheels 60 and 68. The plater then platesthe edges 58 and 64 of the other wheels 60 and 68 and the outerperipheries of the side surfaces of these wheels with fine diamondparticles. In the plated condition, the cross-sections of the wheels arealso ideally exactly complementary to the surfaces 34 and 38 on anenlarged 50× scale. Plating converts one of each of the wheels 60 and 68to a coarse grinding wheel, and the other of each of the wheels 60 and68 to a fine grinding wheel.

The pairs of grinding wheels 60 and 68 then form a 50× enlargement ofthe lens 10. FIGS. 13 and 14 are respective sectional and perspectiveviews illustrating the next steps for this purpose. In FIGS. 13 and 14,the coarse diamond plated surface 58 of the wheel 60 grinds an asphericcylindrical surface 74, corresponding to the surface 34, on a 50× scaleonto a rectangular glass perform block 78. The fine wheel 60 then grindsthe surface 74 to provide it with a fine finish.

To accomplish the grinding operation of the, wheel 60, a magnetic chuck80 in FIGS. 13 and 14 forms part of a surface grinder and holds a steelplate 84. Waxed to the plate 84 is a glass plate 88. The latter carriesthe rectangular block 78 which is waxed to the plate 88. The block 78 isof the same material as the lens 10, and its width is 50 times the widthof the lens 10 in the x-y plane between the surfaces 34 and 38 andacross the cylindrical x-axis. A grinder control 90 rotates the coarsewheel 60 and moves it in and out of the paper in the directions of thedouble headed arrow 94. The grinding operation takes place twice, oncewith the coarse wheel 60 and then with the fine wheel 60.

The process continues by lapping the surface 74. Lapping wheels arefashioned as shown in FIGS. 11 and 12 with a numerically controlleddrive 52. The wheels are treated and then moved by the grinder control90 as shown in FIG. 13 to lap the surface 74 on the block 78. In anembodiment of the invention, the lapping step is omitted.

In FIG. 15, the numerically controlled drive 52 fashions the edge of oneof two grinding wheels 98 to cross-sectional profiles nearly the shapeof the surface 34 on a 50× enlarged scale. A plater then forms coarseand fine wheels by diamond plating the respective edges so theircross-sectional profiles each ideally conforms exactly to the transversecross-section of the surface 34. FIG. 16 shows a plated wheel 98 withthe ideally exact cross-sectional profile 100 of the surface 34.

The block 78 is then removed from the glass, plate 88. FIG. 17 shows thenext step. Here, the control 90 rotates the wheel 98 of FIGS. 15 and 16,and moves it back and forth into and out of the direction of the paper,as shown by the double headed arrow 110, and downwardly to form a groove114 in the plate 88. The control 90 first uses the coarse grinding wheel98 and then the fine grinding wheel. The groove 114 now is ready toreceive a shape corresponding to the surface 34 of the lens 10 enlargedon a 50× scale. In the sectional view of FIG. 18, the block 88 has itsenlarged surface 74, corresponding to the surface 34 of the lens 10,fitted into the groove 114 formed by the arrangement in FIG. 17. Theplate 88 containing the groove 114 remains waxed to the steel plate 84on the magnetic chuck 80 of the surface grinder. Going from FIG. 14 to19 involves flipping over the block 78 and seating the block in thegroove 114. Because the surface 74 and the groove 114 are aspheric,everything lines up. No roll need be accommodated. It is now possible togrind the back surface directly on the block 78.

The lens formation continues as shown in FIG. 19. The latter is aperspective and partially schematic view of the grinding system. Here,the grinder control 90 rotates the grinding wheel 68. The latter has across-section complementary to the shape of the surface 38 in thebiaspheric lens 10 on a 50× scale. The grinder control 90 turns thewheel 68 and moves it back and forth in the directions of the doubleheaded arrow 94 and downwardly against the block 78.

The grinding operation continues as shown in the perspective andpartially schematic view of the grinding system of FIG. 20. The grinderfirst uses the coarse wheel 68, then the fine wheel 68, and finally alapping wheel which received its shape as shown in FIG. 12. Additionalpolishing may also be used to further improve the surface quality. Anoil or water base coolant may be used to cool the surfaces during any orall the grinding and machining operations.

The result is the preform block 78 having the shape of a lens identicalto the lens 10 but on an enlarged 50× scale. The process continues bydrawing the lens down to the dimensions of the lens 10. FIG. 21 is aschematic illustration showing a drawing furnace 124 for drawing thelens shape block 120 into the lens 10.

The drawing furnace uses a careful selection of temperatures, preferablylower, and rates that accurately maintain the profile of the lens formedfrom the block 78. Because the lens grinding process is extremelyaccurate, with or without lapping, the result in surface errors is lessthan a fraction of a micron.

FIG. 22 is a perspective view of a lens 144 embodying the invention andalso having surfaces 34 and 38 shaped and spaced identical to those oflens 10. Here, integral stiffening extensions 148 and 150, between thecylindrical surfaces 34 and 38 project along the x-y plane, i.e., aplane 152, between the surfaces 34 and 38. These extensions 148 and 150serve to stiffen the lens, so the lens 144, when mounted between thelaser strip 20 and aligned ends 24 of the fiber waveguides 28, does notdroop or sag in the x-y plane.

FIG. 23 is a perspective view of a lens 1 64 embodying the invention,and also having surfaces 34 and 38 shaped identically to those of lens10. Here, there are integral stiffening extensions 168 and 170 extendingbetween and beyond the plane 150. These extensions also stiffen thelens.

FIG. 24 is a perspective view of another lens 174 embodying theinvention and having surfaces 34 and 38 corresponding to those of thelens 10. Here, stiffening extensions 178 and 180 extend beyond andbetween the cylindrical surfaces 34 and 38 and project parallel to theplane 150. These extensions 178 and 180 serve to stiffen the lens 174 inthe same manner as the other aforementioned stiffeners by increasing thecross-sectional moment-of-inertia of the lens in the y-z plane.

The lenses in FIGS. 22, 23, and 24 are manufactured from forms at a 50×scale in the manner shown in FIGS. 11 to 16. However, the lapping andgrinding wheels are shaped to cut the form with the extensions. Theextensions 148, 150, 168, 170, 178, and 180 are each tapered and haverounded corners for easy manufacture.

FIG. 25 corresponds to FIG. 14 wherein a grinding wheel 190, having ashape complementary to the surface 34 and the extensions 178 and 180,grinds a block 198 to the proper shape. In FIG. 26, a wheel 200 cuts agroove 204 with extensions into a slab 208 in a manner similar to thatshown in FIG. 17. A wheel 210 in FIG. 27 then grinds the block 198 in amanner similar to that in FIG. 20. The newly ground surface correspondson a 50× scale to the surface 38 with the extensions corresponding to152 and 168 in FIG. 23. This arrangement and process forms the block ofglass having the correct index of refraction to a shape corresponding tothe desired lens 1 64 in FIG. 23. A drawing furnace and tower then drawsthe block 198 axially down at a 50 to 1 reduction in the shape of thelens 198.

What has been shown is how to fabricate a lens that is relativelyinsensitive to tilt and forms a small enough image of a laser diodefacet on the available area of a corresponding entrance end of areceiving fiber so that the overall optical coupling between them isrelatively insensitive to small lateral displacements between therelative positions of the laser diode array and receiving fiber bundle.

Although particular embodiments of the present invention have been shownand described herein, many varied embodiments incorporating theteachings of the present invention may be easily constructed by thoseskilled in the art.

What is claimed is:
 1. An apparatus comprising:a linear laser diodearray containing a plurality of laser diode light sources havingrespective emitting facets; a plurality of optical fiber waveguideshaving respective receiving ends; and optical means for directing lightfrom said emitting facets onto or in said receiving ends, said opticalmeans including a cylindrical lens having two refractive surfaceselongated in a given direction with said surfaces each having acontinuous curvature in a plane transverse to said given direction, oneof said curvatures being aspheric and following a path other than a pathof a conic section.
 2. The apparatus of claim 1 wherein each of saidcurvatures is aspheric and follows a path other than a path of a conicsection.
 3. The apparatus of claim 2 wherein said optical means furtherfunctions for imaging the light from the emitting ends onto thereceiving ends.
 4. The apparatus of claim 3 wherein said lens ispositioned and said surfaces are shaped to converge the light from saidemitting facets onto or into said receiving ends.
 5. The lightgenerating system of claim 4 wherein:said emitting facets of saidplurality of laser diode light sources are aligned parallel to saidgiven direction; and said plurality of receiving ends of said opticalfiber waveguides are aligned parallel to said given direction.
 6. Theapparatus of claim 4 wherein said cylindrical lens has an axis along thegiven direction.
 7. The apparatus of claim 6 wherein said emittingfacets emit diverging light and said fiber waveguides have numericalapertures that define acceptance angles at the receiving ends; andsaidsurfaces of said cylindrical lens are shaped and located to collectdiverging light from the emitting surfaces along one azimuth andconverge it onto or into receiving ends within said acceptance angles ofsaid receiving ends.
 8. The apparatus of claim 7 wherein said surfacescorrect for on- and off-axis aberrations along an azimuth transverse tosaid axis.
 9. The apparatus of claim 8 wherein said surfaces correct forthird and higher order spherical aberrations, coma, and other off-axisaberrations along an azimuth transverse to said axis.
 10. The apparatusof claim 7 wherein said surfaces correct for coma and other off-axisaberrations along an azimuth transverse to said
 11. The apparatus ofclaim 8 wherein said surfaces cooperate together to correct for comaalong an azimuth transverse to the axis.
 12. The apparatus of claim 6wherein said material defines an axis along said elongated direction andsaid surfaces are parallel thereto.
 13. The apparatus of claim 2 whereinsaid material includes stiffening means for stiffening the lens, saidstiffening means including integral extensions projecting from betweensaid surfaces.
 14. The apparatus of claim 13, wherein said stiffeningmeans project in a direction transverse to a plane between saidsurfaces.
 15. A method of making a cylindrical lens having a cylindricalaxis, comprising:shaping the edge of a first grinding wheel with a shapecomplementary to a cross-sectional shape in a plane transverse to theaxis at an enlarged scale; plating said edge of the first grinding wheelwith an abrasive; grinding a cylindrical surface onto a first surface ofa block of a transparent material with said first grinding wheel;shaping the edge of a second grinding wheel with a shape complementaryto a cross-sectional shape in a plane transverse to the axis at saidenlarged scale; plating said edge of the second grinding wheel with anabrasive; grinding a cylindrical surface onto a second surface of saidblock of a transparent material with said second grinding wheel; andheating and drawing down the cylindrical block to the scale of the lens.